This invention relates to gas-liquid contact apparatus, and it particularly pertains to a distributor for distributing liquid onto a bed of packing media.
In a typical gas-liquid contact apparatus, packing media is contained in a sealed, vertically elongated vessel known in the industry as a column or tower. The media may be structured packings such as corrugated sheets of screen or sheet metal, or random particles such as rings or saddles, all of which are well known in the art. Liquid is usually distributed on the upper surface of the packing media by an orifice pan, trough or spray nozzle distributor. Gas is introduced to the vessel through a gas inlet nozzle, and it flows through the packing media where it contacts the liquid on the packing media surfaces before it exits through a gas outlet opening in the vessel. As the liquid moves down through the packing media under the influence of gravitational forces, it wets the surfaces of the packing media, forming a renewing liquid surface to promote the effective contact between the fluids. After the liquid passes through the packing, it flows to a liquid outlet. Normally, the gas flows countercurrent to the liquid flow, but cocurrent arrangements are sometimes used.
The efficiency of a packed column can be severely limited by the performance of the distributor. The quality of liquid distribution is measured in terms of (1) the distribution density, i.e. the number of distribution points per unit of area, (2) the geometric uniformity of distribution points throughout the cross section of the column, and (3) the uniformity of liquid flow from the distribution points.
In a gravitational distributor, the uniformity of liquid flow from the distributor points is significantly affected by entrained vapors and by the head (depth) and velocity of the liquid in the vicinity of the distributor's flow metering liquid outlets. Ideally, there are no entrained vapors, the velocities are negligible, and the heads ar substantially equal at all outlets. Such perfection is not easily attainable with present commercial and design practice methods. The liquid has vertical velocities where it is introduced to the distributor deck, and it often has horizontal velocities as it spreads out in the area of the metering orifices in the distributor deck. The heads across the extent of a distributor deck can also vary widely. Sometimes, there are "dry" outlets where there is little or no liquid head.
Some liquid distribution problems can be alleviated by using slotted flow tubes of the type described in U.S. Pat. Nos. 4,472,325, 4,808,350 or the applicant's U.S. patent application No. 07/363,786, now abandoned. Performance can be improved by forming distributors with multiple partitioned pans and precision die formed flow tubes. However, as liquid flow rates change, the distribution velocity patterns often change significantly.
The present invention makes it possible to achieve satisfactory liquid distribution over a much wider range of flow rates, while substantially improving the uniformity of flow from the distribution points by removing any entrained vapors and, in the vicinities of the distributor's liquid outlet openings, reducing turbulence, reducing horizontal velocities, and reducing head differences.